The lemurs, flying squirrels, and a few other animals have extensions of the skin mantle-wise along the body and legs, to bear them up for a little in the air, as they make long leaps; but they do not really fly. The bat, on the contrary, has good wings, and flies. The bat reminds us a little of that winged reptile which was in the ancient world long before men appeared on the earth. That was a reptile with a large, skin-like wing; a bat is a mammal with two skin-covered wings. The structure of the bat’s wing is very different from that of a bird.[85] The bones and muscles of a bird’s wing are set with stiff feathers, which can be folded together as a fan is furled. When spread they form an elastic instrument for beating the air, and sending the bird forward, upward, downward, wherever it may choose to direct its flight. The body and head of the common bat are very like those of a mouse; it has bright black eyes, a mouth full of tiny white teeth, a covering of gray or reddish hair over all its body. A mouse has a long, scaly tail; a bat has a very short tail; the ears of a mouse are small and pointed; the bat’s ears are large. The nostrils have a fold or ruffle of skin about them, which is supposed to improve the sense of smell. The fore legs, or rather the arms, are very wonderful. If we had the skeleton of a bat we should see that the bones of the arm and forearm are long and slender, and instead of two bones in the lower part or forearm, there is but one which represents the smaller bone in the human arm. The bat’s hand has five distinct fingers. The first of them, the thumb, is short, but the other four are very long, much longer than all the rest of the bat, and they are also very slim. Upon these fingers, as upon a frame, the thin, leather-like double membrane of the wing is stretched on each side of the extended hand, enclosing the finger-bones, thus the two arms have become a pair of wings. This membrane is extended from the fingers to the sides of the body, then passes back to the hind legs, and covers them up to the ankles, and so round enclosing the little tail. Thus the bat has an enormous spread of wing for its size. The long forefinger of the hand extends to the tip of the wing, and the middle finger runs close to it, making this part of the wing strong. When the bat closes its wings the bony frame shuts together like the wires of an umbrella, and the skin hangs in folds as the covering of the umbrella hangs in folds between the closed wires. The thumb of the bat’s hand is left free, and the nail is a large, hooked claw. The flight of a bat is strong and tireless, but it is not in straight lines, nor in easy curves or sweeps like that of a bird; it is restless and flitting, with sharp turns and jerky motions.